clone: add --sparse mode

When someone wants to clone a large repository, but plans to work
using a sparse-checkout file, they either need to do a full
checkout first and then reduce the patterns they included, or
clone with --no-checkout, set up their patterns, and then run
a checkout manually. This requires knowing a lot about the repo
shape and how sparse-checkout works.

Add a new '--sparse' option to 'git clone' that initializes the
sparse-checkout file to include the following patterns:

	/*
	!/*/

These patterns include every file in the root directory, but
no directories. This allows a repo to include files like a
README or a bootstrapping script to grow enlistments from that
point.

During the 'git sparse-checkout init' call, we must first look
to see if HEAD is valid, since 'git clone' does not have a valid
HEAD at the point where it initializes the sparse-checkout. The
following checkout within the clone command will create the HEAD
ref and update the working directory correctly.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/t/t1091-sparse-checkout-builtin.sh b/t/t1091-sparse-checkout-builtin.sh
index 21143c5..78c20cb 100755
--- a/t/t1091-sparse-checkout-builtin.sh
+++ b/t/t1091-sparse-checkout-builtin.sh
@@ -82,4 +82,17 @@ test_expect_success 'init with existing sparse-checkout' '
 	test_cmp expect dir
 '
 
+test_expect_success 'clone --sparse' '
+	git clone --sparse repo clone &&
+	git -C clone sparse-checkout list >actual &&
+	cat >expect <<-EOF &&
+		/*
+		!/*/
+	EOF
+	test_cmp expect actual &&
+	ls clone >dir &&
+	echo a >expect &&
+	test_cmp expect dir
+'
+
 test_done